1. Field of the Invention
The present invention relates to a satellite-tracking antenna controlling apparatus and, more particularly, to a satellite-tracking antenna controlling apparatus installed in a mobile object such as a vehicle, a ship, an airplane, and the like, which communication with a communication satellite.
2. Description of the Related Art
FIG. 9 is a block diagram showing an antenna apparatus according to the related art shown in JP-A-Hei.8-271561, for example. In FIG. 9, reference numeral 1 denotes an antenna for receiving transmitted wave from another antenna arranged to oppose, reference numeral 2 denotes an antenna driving section for changing a directional direction of the antenna 1, reference numeral 3 denotes a transmitting section for transmitting radio wave used to measure the electric field strength, reference numeral 4 denotes a receiving section for receiving a received signal to measure the electric field strength, reference numeral 5 denotes an electric field strength measuring section for measuring the electric field strength, reference numeral 6 denotes a data recording section for recording the measured electric field strength and the measuring time, reference numeral 7 denotes a time matching section for matching the times in a change of the directional direction of the antenna 1, the measurement of the electric field strength, and the data recording, and reference numeral 8 denotes an alignment controlling section for controlling the antenna driving section 2, the transmitting section 3, the electric field strength measuring section 5, the data recording section 6, and the time matching section 7.
When the mobile communication is carried out between two points by using antennas each having the directivity, it is necessary to mutually identify positions of the destination communication devices and to search a direction having the highest received electric field strength to fix the antennas. For this reason, the antenna apparatus according to the related art shown in FIG. 9 receives the transmitted wave transmitted from the destination side via the antenna 1 at a time set previously by the time matching section, and scans the antenna 1 by the antenna driving section 2 at a time of this reception. The received electric field strength is measured by the electric field strength measuring section 5 while the antenna 1 scans and the received electric field strength, the time, and the directional direction of the antenna are recorded by the data recording section 6, and thus the direction of the destination side communication device can be decided based on the resultant data.
Since the antenna apparatus according to the related art is constructed as described above, the alignment of mutual antenna directional directions of the antenna apparatus arranged at two points can be adjusted. However, in the antenna apparatus that executes the communication while changing the relative positional relationship between the mobile object and the communication satellite, in order to direct the antenna to the destination side antenna, in some cases open-loop drive control that drives the antenna based on information of the position and attitude information of the gyro or the like provided to the mobile object and feedback drive control that drives the antenna based on received level are employed in combination. If axial discrepancy is present between a reference axis of a measuring device such as the gyro or the like (normally the gyro or the like is fixed to the mobile object, thus referred to as xe2x80x9can axis of a mobile object-fixed coordinate systemxe2x80x9d hereinafter in this meaning) and an antenna drive axis (referred to as xe2x80x9can axis of a gimbal coordinate systemxe2x80x9d hereinafter), there is a problem that since an error of the directional direction due to the axial discrepancy is generated in the open-loop drive control, the tracking control cannot carried out with high precision. Also, in the antenna apparatus that is installed in an airplane or the like to execute the communication with the satellite, there is a problem that even if an amount of the axial discrepancy between the axis of the mobile object-fixed coordinate system and the axis of the gimbal coordinate system has already been known on a runway of an airport, for example, the amount of the axial discrepancy between the axis of the mobile object-fixed coordinate system and the axis of the gimbal coordinate system are changed much more due to environmental changes such as atmospheric pressure, atmospheric temperature, and the like after takeoff.
The present invention has been made to overcome the above problems and it is an object of the present invention to provide a satellite-tracking antenna controlling apparatus capable of executing satellite-tracking control of an antenna with high precision by calculating an axial discrepancy amount between the mobile object-fixed coordinate system and the gimbal coordinate system of the antenna in case of executing the communication between the mobile object and the communication satellite, and also the satellite-tracking antenna controlling apparatus increasing the maintainability of the axial discrepancy amount.
A satellite-tracking antenna controlling apparatus according to a first aspect of the present invention comprises a satellite direction computing section for computing an azimuth angle and an elevation angle of a satellite in a mobile object-fixed coordinate system fixed to a mobile object based on position information and attitude information of the mobile object, that are output from an inertial navigation unit provided to the mobile object and position information of the satellite as a tracking object, an axial-discrepancy amount correcting section for correcting the azimuth angle and the elevation angle of the satellite computed in the satellite direction computing direction based on an axial discrepancy amount between the mobile object-fixed coordinate system and a gimbal coordinate system of the antenna that is installed in the mobile object to output the corrected azimuth angle and the corrected elevation angle as a drive command signal, a receiver for receiving a signal transmitted from the satellite via the antenna that is driven by the drive command signal, a peak direction drive controlling section for driving the antenna toward a direction in which a level of a received signal received by the receiver becomes peak, an angle sensor for detecting an azimuth angle and an elevation angle of the antenna driven by the peak direction drive controlling section in the gimbal coordinate system, and an axial-discrepancy amount calculating section for computing discrepancy amounts between the azimuth angle and the elevation angle of the antenna in the gimbal coordinate system detected by the angle sensor and the azimuth angle and the elevation angle of the satellite computed by the satellite direction computing section to command the axial-discrepancy amount correcting section to change the axial discrepancy amount.
According to a second aspect of the invention, there is provided the satellite-tracking antenna controlling apparatus according to the first aspect of the invention, wherein the axial-discrepancy amount calculating section commands the axial-discrepancy amount correcting section to change the axial discrepancy amount when the axial-discrepancy amount calculating section decides that the mobile object is going straight on based on the attitude information of the mobile object output from the inertial navigation unit.
According to a third aspect of the invention, there is provided the satellite-tracking antenna controlling apparatus according to the first aspect of the invention, wherein the axial-discrepancy amount calculating section commands the axial-discrepancy amount correcting section to change the axial discrepancy amount when the axial-discrepancy amount calculating section decides that the mobile object has reached a predetermined altitude based on altitude information of the mobile object output from the inertial navigation unit.
According to a fourth aspect of the invention, there is provided the satellite-tracking antenna controlling apparatus according to the first aspect of the invention, wherein the axial-discrepancy amount calculating section commands the axial-discrepancy amount correcting section to change the axial discrepancy amount when the axial-discrepancy amount calculating section decides that a predetermined time has lapsed from a start time of the mobile object.